Microelectronic devices are generally formed on a semiconductor wafer or other type substrate or workpiece. In a typical manufacturing process, one or more thin metal layers are formed on a wafer to produce microelectronic devices and/or to provide conducting lines between devices.
The metal layers are generally applied to the wafers via electrochemical plating in an electroplating processor. A typical electroplating processor includes a vessel or bowl for holding an electroplating solution, one or more anodes in the bowl in contact the electroplating solution, and a head having a contact ring with multiple electrical contacts that touch the wafer. The front surface of the wafer is immersed in the electroplating solution and an electrical field causes metal ions in the electroplating solution to plate out onto the wafer, forming a metal layer.
In so-called “wet-contact” processors, the electrical contacts are exposed to the electroplating solution during a plating cycle. Consequently, the metal ions in the electroplating solution also plate out onto the contacts. The contacts, however, may plate at different rates with the result that some contacts can have a relatively greater or lesser surface area contacting the wafer, as plated-on metal builds up on the contacts over time. This reduces the uniformity of the metal layer plated on the wafer. It can also contaminate the wafer via poorly adhering metal particles separating from the contacts and depositing onto the wafer. To avoid this result, the contacts must be periodically “de-plated” to remove the metal that plates onto the contacts during a plating cycle, as part of ongoing maintenance of the reactor.
Typically, the contacts are deplated by immersing the contact assembly into the plating solution while passing reverse electrical current through them. The reverse current causes the plating cycle to reverse, moving metal off of the contacts and back into the solution. However, the reverse current must be limited to avoid degrading the plating solution. The rate of deplating is also limited by amount of agitation that can be provided to the plating solution around the contacts. Consequently, the contact deplating operation takes significant time to complete.
So-called dry contact electroplating processors use a seal to keep the plating solution away portions of the contacts. The seal must be periodically cleaned to work effectively and avoid contaminating the wafer. The need to maintain the contacts and the seal reduces the throughput or use efficiency of the electroplating system. Accordingly, improved designs are needed.